1. Technical Field
The present invention is related to a battery monitoring system and a semiconductor device.
2. Related Art
High capacity, high output batteries employed in as motor drives in for example hybrid vehicles and electric vehicles generally employ a battery configured from plural serially connected batteries (battery cells). Lithium ion rechargeable batteries are employed for example as such battery cells.
Due to the high energy density of such battery cells, there is the concern that this energy might be instantaneously discharged such as when a problem arises that results in an internal short-circuit. In order to avoid such an occurrence, and in order to avoid abnormal states such as an overcharged state or an excessive discharge state, battery voltage monitoring of the battery cells is performed by a battery monitoring system. Examples of such battery monitoring systems include the technology disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2009-100644, JP-A No. 2010-178400, and JP-A No. 2010-281717.
The battery monitoring systems of JP-A No. 2009-100644, JP-A No. 2010-178400 and JP-A No. 2010-281717 are provided with plural battery monitoring semiconductor devices (ICs) that monitor each collection (battery cell set) in a configuration wherein plural serially connected battery cells are divided into collections each containing a specific number of battery cells.
The battery monitoring systems described above are configured such that plural the battery monitoring ICs are connected to the plural serially connected battery cells.
Each battery monitoring IC includes a voltage measuring section that measures battery cell battery voltage, a high side communication section that performs communication with a battery monitoring IC that monitors a higher position battery cell set, a low side communication section that performs communication with a battery monitoring IC that monitors a lower position battery cell set, and a communication level converter that converts the voltage levels of the high side communication section and the low side communication section.
Each battery monitoring IC operates employing a battery voltage of each of the battery cell sets to be monitored. In order to perform communication between the respective battery monitoring ICs there is a need to match the voltage levels employed for signals during communication between the respective battery monitoring ICs since the battery voltage levels of each of the battery cell sets to be monitored are different from each other. The communication level converter accordingly performs conversion between the voltage levels of the high side communication section and the low side communication section.
In such battery monitoring systems, for example the battery monitoring IC that monitors the lowest position battery cell set receives for example a control signal from a controller in the low side communication section, converts the voltage level in the communication level converter, and then transmits the control signal from the high side communication section to the low side communication section of the battery monitoring IC that monitors a higher position battery cell set. Each of the battery monitoring ICs accordingly receives signals in the low side communication section, performs voltage conversion in the communication level converter, and transmits signals from the high side communication section. However, there is no need to operate the communication level converter or the high side communication section of the battery monitoring IC that monitors the highest position battery cell set since there is no higher position battery monitoring IC present.
There is accordingly the issue that current for operating the communication level converter and the high side communication section of the highest position battery monitoring IC is wasted.